TRANSMISSION PROBLEMS

I have a 2001 XJ8L. After I first put the car into drive, the gears shift slowly and then slam into drive, and then the transmission fault message appears on the dash screen. It still runs fine after first gear, and won't slam into first gear any more unless the car is re-started.

The repair shop I took the car to said it needs a new transmission. Is this the case or can a less costly repair be made?